Just melt the butter and toss all the vegetables except the peas and the lettuce in it together with the bouquet. Stir in the flour very gently. Add the stock and white wine and sugar. Cover and simmer for 10 minutes. Add the heart of the washed lettuce cut into strips and the peas, and simmer for another 10 minutes or till all the vegetables are tender. Remove from heat and stir in the cream.